Viewing Nicotine’s Effects on the Embryo at the Cellular Level

That maternal smoking during pregnancy can cause harmful effects likely does not come as a surprise to many. It is well known that nicotine can cause gestational complications and organ disorders, but the mechanisms for these effects on the developing human embryo remain poorly understood. In a new study, researchers used single-cell RNA sequencing to observe how nicotine exposure disrupts cell-to-cell communication, decreases cell survival, and alters gene expression regulating critical functions such heart muscle-cell contractions. Their findings were published today in Stem Cell Reports.

The authors credit their findings to a new stem-cell model involving human embryonic stem cell (hESC)-derived embryoid bodies, which are 3D aggregates of different types of pluripotent cells that give rise to the brain, heart, liver, blood vessels, and other organs. This allowed them to circumvent animal models as these can’t always be translated to human systems. Furthermore, previous studies have used conventional RNA sequencing, preventing understanding effects in single cells.

Use of single-cell RNA sequencing in the current study allowed the researchers to analyze the effects of 21 days of nicotine exposure on the transcriptomes of 12,500 cells generated from hESC-derived embryoid bodies. During this time cell survival decreased, suggesting nicotine can affect the embryo even in the preimplantation stage.

Other findings from the study revealed nicotine exposure can decrease the size of the embryoid bodies, increase levels of reactive oxygen species, and result in aberrant formation and differentiation of embryoid bodies. Nicotine exposure also altered cell cycling in a range of progenitor cells and caused dysregulated cell-to-cell communication. These findings give a mechanistic explanation for the increased risk of disruptions in endocrine, reproductive, respiratory, cardiovascular, and neurologic systems due to maternal smoking and nicotine use.

The researchers also found alteration of gene expression linked to a number of pathologies including metal toxicity and mitochondrial function, brain malformations, muscle development, and lung disease among others.

While the researchers acknowledge the limitations of the system in not being able to account for whole-body physiology, they believe it is still a helpful system for understanding toxicity and environmental effects on the human embryo. "We hope this will lead to the discovery of novel biomarkers that can help doctors better prevent, diagnose, and treat these diseases," said senior author Joseph C. Wu of the Stanford University School of Medicine.

Image: This image illustrates how researchers studied the adverse effects of nicotine exposure on various cell lineages derived from human embryonic stem cells using single-cell RNA sequencing (scRNA-seq). Image courtesy of Hongchao Guo.